From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E321BC433E0 for ; Mon, 11 Jan 2021 16:23:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9962822AAD for ; Mon, 11 Jan 2021 16:23:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388513AbhAKQXS (ORCPT ); Mon, 11 Jan 2021 11:23:18 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2306 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388683AbhAKQXR (ORCPT ); Mon, 11 Jan 2021 11:23:17 -0500 Received: from fraeml736-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4DDzR95cl6z67Yr5; Tue, 12 Jan 2021 00:18:45 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml736-chm.china.huawei.com (10.206.15.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Mon, 11 Jan 2021 17:22:35 +0100 Received: from [10.210.171.188] (10.210.171.188) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2106.2; Mon, 11 Jan 2021 16:22:34 +0000 From: John Garry Subject: About scsi device queue depth To: Ming Lei , Bart Van Assche , Hannes Reinecke , Kashyap Desai , "Martin K . Petersen" , "James E.J. Bottomley" , Christoph Hellwig , "linux-scsi@vger.kernel.org" , Sathya Prakash , Sreekanth Reddy , Suganath Prabu Subramani , PDL-MPT-FUSIONLINUX CC: chenxiang Message-ID: <9ff894da-cf2c-9094-2690-1973cc57835a@huawei.com> Date: Mon, 11 Jan 2021 16:21:27 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.171.188] X-ClientProxiedBy: lhreml703-chm.china.huawei.com (10.201.108.52) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org Hi, I was looking at some IOMMU issue on a LSI RAID 3008 card, and noticed that performance there is not what I get on other SAS HBAs - it's lower. After some debugging and fiddling with sdev queue depth in mpt3sas driver, I am finding that performance changes appreciably with sdev queue depth: sdev qdepth fio number jobs* 1 10 20 16 1590 1654 1660 32 1545 1646 1654 64 1436 1085 1070 254 (default) 1436 1070 1050 fio queue depth is 40, and I'm using 12x SAS SSDs. I got comparable disparity in results for fio queue depth = 128 and num jobs = 1: sdev qdepth fio number jobs* 1 16 1640 32 1618 64 1577 254 (default) 1437 IO sched = none. That driver also sets queue depth tracking = 1, but never seems to kick in. So it seems to me that the block layer is merging more bios per request, as averge sg count per request goes up from 1 - > upto 6 or more. As I see, when queue depth lowers the only thing that is really changing is that we fail more often in getting the budget in scsi_mq_get_budget()->scsi_dev_queue_ready(). So initial sdev queue depth comes from cmd_per_lun by default or manually setting in the driver via scsi_change_queue_depth(). It seems to me that some drivers are not setting this optimally, as above. Thoughts on guidance for setting sdev queue depth? Could blk-mq changed this behavior? Thanks, John